DESCRIPTION (Investigator's Abstract): The long term goal of this project is to understand how finger muscles produce individuated finger movements--those in which one or more fingers are moved without moving the others. Though each finger often is assumed to be moved by its own muscles, the extrinsic muscles that provide most of the flexing and extending power typically send tendons to multiple fingers. This anatomic fact presents a paradox: contractions of these multitendoned muscles should move multiple fingers simultaneously. Individuated flexion and extension of the fingers are hypothesized to be possible because: i) functional subdivisions within some multitendoned muscles may apply tension relatively selectively to some of the muscle's tendons, and ii) the forces produced by different multitendoned muscles may combine such that the net forces on each finger cause one digit to move while other digits are held still. The proposed studies specifically aim to address the following 6 questions: 1) Does each neuromuscular compartment in multitendoned finger muscles distribute tension to more than one tendon? 2) Do single motor units in these muscles distribute tension to multiple tendons? 3) Do mechanical interconnections between a muscle's tendons passively distribute tension to multiple fingers? 4) Do single motor units in human finger muscles act on multiple fingers? 5) Do humans co-contract several multitendoned finger muscles to produce individuated movement of one finger while holding other fingers still? 6) Can the mechanical action of several multitendoned muscles combine to move one finger while holding the other fingers still? These studies will result in an improved basic understanding of how multitendoned finger muscles function, which can translate into: i) production of useful finger movements by functional electrical stimulation of these muscles in patients with brain or spinal cord injury, ii) more accurate botulinum toxin injections for treatment of the hand's focal dystonias, and iii) more appropriate tendon transfers for reconstruction of a useful hand in patients debilitated by forearm trauma. Moreover, results of the proposed studies of muscles will have broad implications for understanding how finger movements are controlled by the central nervous system.